Moisture content of feed grains is believed to be critically important to the quality and palatability of most finished feed products. It may also have a significant impact on the ease with which they are processed into feed, but has been a largely uncontrolled variable in most animal feed manufacturing processes. Moisture levels encountered typically range between eight and sixteen percent in stored grain. New crop grains may have moisture levels in excess of twenty percent. A feed manufacturing facility will commonly process several hundreds of tons of feed grains each day that have been purchased from many sources. Within a matter of minutes the moisture content of the grain being processed can vary several percentage points. Without regulated moisture addition, a highly variable feed product is produced.
The processing of feed grains in the manufacturing of finished livestock feeds is intended to increase the feed value of the grains. "Value" may be defined in terms of palatability and digestibility. The efficiency and profitability of modern livestock enterprises are based in large part on the weight ratio between incoming grain and outgoing product. Incremental improvements in that ratio, which may be generated by improved grain processing methods to eliminate waste and to optimize digestibility, will directly effect the profitability of the livestock operation.
The most simple processing involves either the grinding or dry rolling of the whole kernel grain to fracture the seed coat and to increase the surface area of the grain particles for more efficient digestion. Grain moisture content greatly affects the texture of the final products produced by these dry methods. Very dry grain will tend to make flour, which the animals will not consume readily and typically prefer a larger particle. This flour, or dust, represents a safety hazard in the feed manufacturing facility, both from the explosion potential and from workers breathing it. It also represents a loss of product to the feed manufacturer. Careful control of the moisture level of the grain entering these dry processes can eliminate dust and help to produce a uniform particle size that will improve digestion without being so small as to depress consumption. Livestock feeds are commonly prepared with dry processed grain.
A more sophisticated method of processing feed grains involves cooking them with steam before they are passed through a roller mill (or flaking mill). The cooking process partially gelatinizes the starch in the grain, increasing its digestibility. The rolling step increases surface area of the grain kernel by pressing it into a flat "flake" and also increases gelatinization of the starch matrix. Beef and dairy cattle feeds are commonly steam flaked. Whole kernel grain flows through a chamber into which live steam is injected. Once "cooked", it passes through a roller mill, producing a "flake". If the grain is too dry, the cooking or gelatinizing will be incomplete, since the gelatinizing process requires heat, free moisture and mechanical disruption of the starch matrix. The grain kernel will be hard and will require more energy to roll than a moist, properly cooked kernel. The final flake will be dry and brittle. Subsequent handling of the flake will cause it to break, resulting in "fines" that the animal will not eat readily.
A second processing method involving steam cooking of the grain is pelleting, which is commonly used to prepare poultry feeds. The grain is ground to a uniform texture, mixed with other feed ingredients and treated with steam. The resulting mash is extruded through a die in a pellet mill. As with steam flaking, gelatinization, toughness and durability of the final feed form, are greatly influenced by the moisture content of the grains being processed. The power required to drive the pellet mill, as well as machine life, is also affected by the moisture content of the mash. If it is too dry, more power will be required to extrude the pellet, the cooking will be incomplete and the feed ingredients will not bond well, causing a weak pellet that falls apart. Broken pellets become "fines" that are not eaten and represent a loss to the livestock producer.
U.S. Pat. Nos. 4,898,092 and 4,994,286 (the Greer patents), which were filed in 1988 and 1990, respectively, describe methods for conditioning feed grains and seed grains, including the application of water to the grains to attain a target moisture level. The disclosures of both of the Greer patents are hereby incorporated herein by reference. Greer discloses a method for automatically adding moisture to grains by determining the moisture content of the incoming grain and then adding water (or other liquid) to the grain based on that incoming moisture level.
Greer's systems are feed-forward or predictive systems, and they do not provide for automated measurement of the actual moisture level in the grain after it has been wetted, or at any point later in the process of preparing a feed grain for consumption by livestock. A later Greer patent, U.S. Pat. No. 5,194,275, is also incorporated herein by reference. The Greer '275 patent adds mass flow rate detection to the control system in order to control the rate of liquid application based on both the moisture level of the incoming grain as well as the mass flow rate of the grain.
U.S. Pat. No. 5,133,982 is also incorporated herein by reference. It discloses a grain conditioning system that adds liquid to a grain flow based on feedback from a moisture sensor placed downstream from the liquid applicator. The sensor detects the actual moisture level after liquid addition and mixing. Both bypass and full-stream moisture detection systems are disclosed.
In view of the prior art discussed herein, there is a need for a more efficient feed processing system that provides a consistently optimal quality feed product, regardless of the type and condition of the grain introduced into the processing system. The desired system would incorporate moisture sensors and other sensors throughout the processing system, in order to implement a multi-level, intelligent feedback control system that would provide optimal control over the quality of the finished product.